Conventionally, relating to a display device, a method of providing an input function such as a touch panel, pen input, or a scanner by providing a plurality of optical sensors in a display panel has been known. Recently, particularly a display device obtained by a method in which light receiving elements such as photodiodes are formed in a pixel region concurrently when semiconductor elements of display pixels are formed in a pixel region has been known widely as well (see, for example, the gazette of JP2006-3857, the gazette of WO2007/145346, and the gazette of WO2007/145347).
In the case where optical sensors are provided in a pixel region, however, bus lines for supplying driving signals to optical sensors are needed in addition to bus lines (lines) for supplying driving signals to display pixel circuits in the pixel region, which decreases the pixel aperture ratio.